all credit to head_victim in #lubuntu
Right now, all testers see after installing the alpha release is a
black screen with a "failed to load session ubuntu"
there is a workaround:
control+alt+f1 (if you are using a vm you will need to know secret
codes control+alt space, control+alt f1)
(login to the console)
sudo apt-get install lxdm
sudo reboot
alt+L to get past the error again
change the session to lubuntu
login